A usual design of a side airbag module includes a gas generator mounted inside a cavity in a side bolster of a back rest of a vehicle seat. The gas generator is mounted on a backside of the seat cavity and projects inflation gas in a forward direction of the vehicle. In the seat cavity, a folded airbag is arranged around and attached to the gas generator. The seat cavity is enclosed by a cover made of a molded shell of optically appealing plastic material that conceals the airbag module. The cover forms a visible surface of the back rest. The cover has an intentionally weakened seam or line of reduced thickness designed to break when the gas generator inflates the airbag.
The cover forms a Class A surface. Class A surface areas are those that remain visible when the part is installed on the vehicle when all mating components, such as hoods, doors, and trunk lids, are in a closed position. Standards for Class A surfaces may vary by manufacturer and generally specify permissible parameter ranges for aesthetically pleasing appearance without posing an elevated injury risk upon impact. For example, for Class A surfaces, excessive roughness, sharp edges, and sharp corners are not permissible. Class A surfaces have curvature and tangency alignment, which means that not only the surface must be mathematically continuous, but also its curvature radius. Thus, Class A surfaces to have at least a so-called G2 curvature continuity, possibly or even a G3 curvature continuity that also requires a change of the curvature radius to be mathematically continuous.
The above-described known airbag arrangement, in which the gas generator is mounted in the side bolster of the vehicle seat back, has the disadvantage that each part of the gas generator must be individually attached to a fastening structure inside the seat cavity that may not be easily accessible for assembly.